1. Field of the Invention
This invention relates to a part of an office machine, and more particularly to a knuckle arm that interconnects a machine body and a top cover of an office machine.
2. Description of the Related Art
Two knuckle arms are typically disposed between a top cover and a machine body of an office machine, such as a copier, or scanner, for use in the opening and closing of the top cover relative to the machine body. Referring to FIG. 1, a conventional knuckle arm 10, which is disclosed in U.S. Pat. No. 6,456,365, is shown to include a mounting seat 11 fixed on a machine body 21 of an office machine 20, a connecting seat 12 disposed pivotally on the mounting seat 11, a bottom cam sliding seat 13 disposed slidably within the connecting seat 12, a top cam sliding seat 14 disposed slidably within the connecting seat 12 and located above the bottom cam sliding seat 13, a compression spring 15 disposed between the bottom and top cam sliding seats 13, 14, a lifting seat 16 disposed pivotally on the connecting seat 12 and connected fixedly to a top cover 22 of the office machine 20, a bottom pivot rod 17 extending through the mounting seat 11 and the connecting seat 12 and kept in contact with a cam surface 131 of the bottom cam sliding seat 13, and a top pivot rod 18 extending through the connecting seat 12 and kept in contact with a cam surface 141 of the top cam sliding seat 14.
As such, a force can be applied to the top cover 22 so as to open and close the top cover 22 relative to the machine body 21. Although the knuckle arm 10 can achieve its intended purposes, in actual use, it suffers from the following disadvantages:                (1) Since the total weight of the lifting seat 16, the connecting seat 12, the top cam sliding seat 14, the spring 15 and the bottom cam sliding seat 13 is significant, the user must exert a large force to open and close the top cover 22. This particularly burdensome when the top cover is opened or closed with one hand.        (2) Lubrication oil is applied between the connecting seat 12 and each of the top and bottom cam sliding seats 14, 13 so as to enable smooth movement of the top and bottom cam sliding seats 14, 13 within the connecting seat 12. However, because the connecting seat 12 as well as the top and the bottom cam sliding seats 14, 13 are disposed outwardly of the mounting seat 11, the lubrication oil may stain the paper, documents, etc. used in the office machine 20.        (3) There is a need for high precision during manufacture of the cam surfaces 131, 141 of the bottom and top cam sliding seats 13, 14. The processes required to achieve such high precision ultimately result in high manufacturing costs of the knuckle arm 10.        